There has been conventionally known a sheet feeder having a function to detect the remaining amount of a roll of paper as disclosed in, for example, Japanese Patent Application Publication No. 2007-76849. Such a sheet feeder detects the remaining amount of a roll of paper by calculating a distance from a contact member that is in contact with the roll of paper to the bottom surface based on the rotation angle of a rotary switch.
In addition, a thermal printer having a thermal print unit is widely used as a mobile printer, an ATM, a KIOSK terminal, or a convenience store payment terminal printer. In the case where the administrator cannot reside and the timing for replacing a roll of paper is limited like ATM, implementation of a mechanism for detecting the state where the remaining amount of paper is small, that is, the so-called near-end of a roll of paper is desired.
There has been known a technique that detects the outside diameter of a roll of paper by attaching a switch or an optical sensor to the side surface or the bottom surface of a paper holder to detect the near-end of a roll of paper.